Programmed Cell Death 1 or PD-1 (also referred to as PDCD1) is a 50 to 55 kD type I membrane glycoprotein (Shinohara T et al, Genomics, 1994, Vol. 23, No. 3, pp. 704-706). PD-1 is a receptor of the CD28 superfamily that negatively regulates T cell antigen receptor signalling by interacting with the specific ligands and is suggested to play a role in the maintenance of self tolerance.
PD-1 peptide relates to almost every aspect of immune responses including autoimmunity, tumour immunity, infectious immunity, transplantation immunity, allergy and immunological privilege.
The PD-1 protein's structure comprise of—                an extracellular IgV domain followed by        a transmembrane region and        an intracellular tail        
The intracellular tail contains two phosphorylation sites located in an immunoreceptor tyrosine-based inhibitory motif and an immunoreceptor tyrosine-based switch motif, which suggests that PD-1 negatively regulates TCR signals. Also, PD-1 is expressed on the surface of activated T cells, B cells, and macrophages, (Y. Agata et al., Int Immunol 8, 765, May 1996) suggesting that compared to CTLA-4 ((Cytotoxic T-Lymphocyte Antigen 4, also known as CD152 (Cluster of differentiation 152) is a protein that also plays an important regulatory role in the immune system), PD-1 more broadly negatively regulates immune responses.
PD-1 has two ligands, PD-L1 (Programmed Death Ligand 1 or PDCD1L1 or B7-H1) (Freeman G J et al, Journal of Experimental Medicine, 2000, Vol. 19, No. 7, pp. 1027-1034) and PD-L2 (Programmed Death Ligand 2 or PDCD1L2 or B7-DC) (Latchman Y et al, Nature Immunology, 2001, Vol. 2, No. 3, pp. 261-267), which are members of the B7 family. PD-L1 is known to be expressed not only in immune cells, but also in certain kinds of tumour cell lines (such as monocytic leukaemia-derived cell lines, mast cell tumour-derived cell lines, hematoma-derived cell lines, neuroblastoma-derived cell lines, and various mammary tumour-derived cell lines) and in cancer cells derived from diverse human cancer tissues (Latchman Y et al, Nature Immunology, 2001, Vol. 2, No. 3, pp. 261-267) and on almost all murine tumour cell lines, including PA1 myeloma, P815 mastocytoma, and B16 melanoma upon treatment with IFN-γ (Y. Iwai et al., Proc Natl Acad Sci USA 99, 12293, Sep. 17, 2002 and C. Blank et al., Cancer Res 64, 1140, February, 2004). Similarly PD-L2 expression is more restricted and is expressed mainly by dendritic cells and a few tumour cell lines. PD-L2 expression has been verified in Hodgkin's lymphoma cell lines and others. There is a hypothesis that some of the cancer or tumour cells take advantage from interaction between PD-1 and PD-L1 or PD-L2, for suppressing or intercepting T-cell immune responses to their own (Iwai Y et al, Proceedings of the National Academy of Science of the United States of America, 2002, Vol. 99, No. 19, pp. 12293-12297).
Tumour cells and virus (including HCV and HIV) infected cells are known to express the ligand for PD-1 (to create Immunosuppression) in order to escape immune surveillance by host T cells. It has been reported that the PD-1 gene is one of genes responsible for autoimmune diseases like systemic lupus erythematosis (Prokunina et al, Nature Genetics, 2002, Vol. 32, No. 4, 666-669). It has also been indicated that PD-1 serves as a regulatory factor for the onset of autoimmune diseases, particularly for peripheral self-tolerance, on the ground that PD-1-deficient mice develop lupus autoimmune diseases, such as glomerulonephritis and arthritis (Nishimura H et al, International Immunology, 1998, Vol. 10, No. 10, pp. 1563-1572; Nishimura H et al, Immunity, 1999, Vol. 11, No. 2, pp. 141-151), and dilated cardiomyopathy-like disease (Nishimura H et al, Science, 2001, Vol. 291, No. 5502, pp. 319-332).
Hence, in one approach, blocking the interaction of PD-1 with its ligand (PD-L1, PD-L2 or both) may provide an effective way for specific tumour and viral immunotherapy.
Wood et al in U.S. Pat. No. 6,808,710 discloses method for down modulating an immune response comprising contacting an immune cell expressing PD-1 with an antibody that binds to PD-1, in multivalent form, such that a negative signal is transduced via PD-1 to thereby down modulate the immune response. Such an antibody may be a cross-linked antibody to PD-1 or an immobilized antibody to PD-1.
Freeman et al in U.S. Pat. No. 6,936,704 and its divisional U.S. Pat. No. 7,038,013 discloses isolated nucleic acids molecules, designated B7-4 nucleic acid molecules, which encode novel B7-4 polypeptides, isolated B7-4 proteins, fusion proteins, antigenic peptides and anti-B7-4 antibodies, which co-stimulates T cell proliferation in vitro when the polypeptide is present on a first surface and an antigen or a polyclonal activator that transmits an activating signal via the T-cell receptor is present on a second, different surface.
There are some reports regarding substances inhibiting immunosuppressive activity of PD-1, or interaction between PD-1 and PD-L1 or PD-L2, as well as the uses thereof. A PD-1 inhibitory antibody or the concept of a PD-1 inhibitory peptide is reported in WO 01/14557, WO 2004/004771, and WO 2004/056875. On the other hand, a PD-L1 inhibitory antibody or a PD-L1 inhibitory peptide is reported in WO 02/079499, WO 03/042402, WO 2002/086083, and WO 2001/039722. A PD-L2 inhibitory antibody or a PD-L2 inhibitory peptide is reported in WO 03/042402 and WO 02/00730.
WO2007005874 describes isolated human monoclonal antibodies that specifically bind to PD-L1 with high affinity. The disclosure provides methods for treating various diseases including cancer using anti-PD-L1 antibodies.
US2009/0305950 describes multimers, particularly tetramers of an extracellular domain of PD-1 or PD-L1. The application describes therapeutic peptides.
Further, the specification mentions that peptides can be used therapeutically to treat disease, e.g., by altering co-stimulation in a patient. An isolated B7-4 or PD-1 protein, or a portion or fragment thereof (or a nucleic acid molecule encoding such a polypeptide), can be used as an immunogen to generate antibodies that bind B7-4 or PD-1 using standard techniques for polyclonal and monoclonal antibody preparation. A full-length B7-4 or PD-1 protein can be used, or alternatively, the invention provides antigenic peptide fragments of B7-4 or PD-1 for use as immunogens. The antigenic peptide of B7-4 or PD-1 comprises at least 8 amino acid residues and encompasses an epitope of B7-4 or PD-1 such that an antibody raised against the peptide forms a specific immune complex with B7-4 or PD-1. Preferably, the antigenic peptide comprises at least 10 amino acid residues, more preferably at least 15 amino acid residues, even more preferably at least amino acid residues, and most preferably at least 30 amino acid residues.
Freeman et al in U.S. Pat. No. 7,432,059 appears to disclose and claim methods of identifying compounds that up modulate T cell activation in the presence of a PD-1-mediated signal. Diagnostic and treatment methods utilizing compositions of the invention are also provided in the patent.
Further, Freeman et al in U.S. Pat. No. 7,709,214 appears to cover methods for up regulating an immune response with agents that inhibit the interactions between PD-L2 and PD-1.
Despite existence of many disclosures as discussed above, however, a significant unmet medical need still exists due to the lack of effective peptides or modified peptides as therapeutic agents as alternatives in the therapeutic area. It is known that synthetic peptides offer certain advantages over antibodies such as ease of production with newer technologies, better purity and lack of contamination by cellular materials, low immunogenicity, improved potency and specificity. Peptides may be more stable and offer better storage properties than antibodies. Moreover, often peptides possess better tissue penetration in comparison with antibodies, which could result in better efficacy. Peptides can also offer definite advantages over small molecule therapeutics counterparts such as lesser degree of toxicity and lower probability of drug-drug interaction.
The present invention therefore may provide the solution for this unmet medical need by offering novel synthetic peptide and its derivatives which are based on the PD1 ectodomain.